There has been known a communication apparatus including a plurality of transmitter for transmitting electromagnetic waves or a plurality of receivers for receiving electromagnetic waves. In such a communication apparatus, a phase calibration is carried out on the signals transmitted through the plurality of transmitters or the plurality of receivers to adjust a phase difference between the transmitted signals to a desired phase difference.
For performing the phase calibration, the communication apparatus includes a phase adjuster in each of the plurality of transmitter or in each of the plurality of receivers. The phase adjuster adjusts the phase of a signal transmitted through each of the plurality of transmitters or each of the plurality of receivers, and outputs a phase-adjusted signal to a mixer. The mixer synthesizes two signals received from two adjacent phase adjusters, respectively, to generate a detection signal for detecting a phase difference between the two signals and outputs the detection signal thus generated to a phase controller. The detection signal generated by the mixer has the maximum sensitivity phase difference where the detection sensitivity of a phase difference becomes maximum. A detection sensitivity of phase difference corresponds to a slope of the waveform of a detection signal. For example, it is assumed that the waveform of a detection signal exhibits a cosine curve. The cosine curve indicates that the characteristics of a detection signal is expressed as a cosine waveform (the signal level (amplitude or power) of the detection signal has a cosine waveform with respect to the phase difference). The detection sensitivity of phase difference becomes maximum at a point where a derivative of the signal level of a detection signal with respect to phase difference (the slope of the waveform) becomes maximum, and the detection sensitivity at the point is the maximum sensitivity phase difference. In this case, the maximum sensitivity phase difference is obtained at ±π/2 where the slope of the cosine curve becomes maximum. The phase controller controls the amount of phase-adjusting by two adjacent phase adjusters so that the difference between a phase difference detected within a predetermined range around the maximum sensitivity phase difference by using the detection signal received from the mixer and the preset phase difference is zero.
Related technologies are disclosed in, for example, Japanese Laid-Open Patent Publication No. 2013-34129, Japanese Laid-Open Patent Publication No. 2010-54218.